WO2015069516A1

WO2015069516A1 - Switched-capacitor split drive transformer power conversion circuit

Info

Publication number: WO2015069516A1
Application number: PCT/US2014/062859
Authority: WO
Inventors: Minjie Chen; David J. Perreault; Khurram K. AFRIDI
Original assignee: Massachusetts Institute Of Technology
Priority date: 2013-10-29
Filing date: 2014-10-29
Publication date: 2015-05-14
Also published as: US9825545B2; US20160190943A1

Abstract

A split drive transformer (SDT) and use of such a transformer in a power converter is described. The power converter includes a power and distributor circuit configured to receive one or more input signals and provides multiple signals to a first side of the SDT. The SDT receives the signals provided to the first side thereof and provides signals at a second side thereof to a power combiner and rectifier circuit which is configured to provide output signals to a load. In some embodiments, the SDT may be provided as a switched-capacitor (SC) SDT. In some embodiments, the power converter may optionally include a level selection circuit (LSC) on one or both of the distributor and combiner sides.

Description

SWITCHED-CAPACITOR SPLIT DRIVE TRANSFORMER POWER CONVERSION CIRCUIT

FIELD

[0001] This disclosure relates generally to power converter circuits and more particularly, to the use of a transformer, inverter and rectifier structures and controls for use in power converter circuits.

BACKGROUND

[0002] As is known in the art, power supplies for dc distribution systems, computers, telecommunications and data centers, as well as for transportation, lighting, displays, and medical applications among many other areas require high power density and fast response, provide electrical isolation and operate efficiently. In many cases, there is a desire for efficiency at high conversion ratios and/or over wide operating ranges (of voltages and/or powers). There is also a desire to achieve a high degree of integration, manufacturability and reliability. Traditionally, magnetic converter-based architectures with isolation transformers are widely used, such as forward converters, flyback converters and related architectures. Such architectures are simple, low-cost and easy to control. There is, however, a continued trend to operate power converters at ever increasing switching frequencies and as switching frequencies increase the converter timing required in the aforementioned architectures becomes difficult to satisfy, and the parasitic effects significantly increase the loss.

[0003] As is also known, circuits using high-gain transformers or coupled inductors is one approach to building converters in these applications. Circuits incorporating tapped inductors can provide desirable duty ratios and reduces device switching stress. However, the leakage inductance of such tapped inductors can ring with the parasitic capacitance of the switches, limiting its feasibility at high switching frequency. High-frequency-link architectures can reduce or eliminate this ringing problem by absorbing parasitics such as transformer leakage inductance into circuit operation. Such circuits can often also realize soft switching and switch at a higher frequency than conventional hard- switched architectures.

[0004] Nevertheless, as desired operating switching frequencies keep increasing, parasitic effects which are sometimes ignored, such as the proximity effect loss and transformer parasitic capacitances, can become very important. Furthermore, requirements that a system achieve high performance over wide operating range makes the system design even more challenging.

SUMMARY

[0005] In accordance with the concepts, systems, circuits and techniques described herein it has been recognized that new converter architectures and associated controls are required to overcome the aforementioned challenges.

[0006] In one aspect, the power conversion circuits and techniques described herein utilize an architecture which incorporates an advanced transformer structure referred to herein as a split-drive transformer (SDT). The SDT structure architecture reduces transformer parasitic effects (e.g. in particular, the effects of parasitic capacitance, although parasitic inductance and resistance characteristics may also exist), and absorbs the transformer parasitics into circuit operation.

Reducing, and ideally eliminating, the effect of such transformer parasitic

components enables the transformer to operate closer to their ideal transformer characteristics. Moreover, the SDT architecture described herein utilizes the transformer together with a circuit power stage (referred to herein as a power distributor stage) to process the power in multiple voltage domains, and to compress the required operation range of each voltage domain, thus enabling the power converter to work efficiently over wider operation range.

[0007] In prior art techniques, the transformer proximity effect and parasitic capacitances set a barrier for increasing the switching frequency of an isolated power converter. [0008] The concepts, circuits, systems and techniques described herein overcome these barriers through use of a system architecture incorporating an advanced transformer structure (e.g. the aforementioned SDT structure) and appropriate inverter and rectifier structures and controls. This approach reduces transformer loss and opens the opportunity of building efficient, isolated power converters capable of operation at switching frequencies which are much higher than that at which conventional designs can operate.

[0009] Power converters provided in accordance with the concepts described herein are also capable of operating at higher efficiency and power density than conventional designs.

[00010] In one aspect a power conversion circuit includes a distributor and inverter stage coupled to a combiner and rectifier stage through a split drive transformer (SDT) stage which operates to step up/down voltage provided thereto and provide isolation between the distributor and combiner stages. The power distributor and inverter stage has either or both of the following two functions: to receive the overall input power and voltage from a source, condition it and distribute it to multiple paths to interface with the split-drive transformer stage; and/or maintain the variation of its outputs within a narrow range even if its input has relatively variations. This function enables the remainder of the converter to be optimized for a compressed operating range, leading to a higher efficiency of the overall system.

[0001 1] One or more of the following features may be incorporated, individually or in combination and in whole or in part, into various embodiments. In embodiments the power distribution and inverter stage comprises switch and gate drive circuit. In embodiments, the power distribution and inverter stage comprises one or more full or half- bridge switching circuits. In embodiments, the split drive transformer stage receives n ac drive waveforms from the distributor. In embodiments, the split drive transformer stage has an interleaved configuration. In embodiments, the split drive transformer stage is provided having a single-phase balancer configuration (i.e., not an interleaved one) and/or only uses a single phase of the interleaved balancer to synthesize the inverter drive outputs. This would have the advantage of reducing the ac drive amplitudes produced by the inverter cells. In embodiments, the split-drive transformer stage uses magnetic coupling to step up/down the voltage and provide isolation.

[00012] In embodiments, the combiner and rectifier stage are provided having parallel coupled outputs. In embodiments, the combiner and rectifier stage are provided having series coupled outputs.

[00013] In embodiments, the combiner and rectifier stage are provided having half bridge switching cells. In embodiments, the combiner and rectifier stage are provided having full bridge switching cells

[00014] In embodiments, a switched-capacitor SDT converter (SCSDT converter) is provided having a centralized rectifier. In embodiments, the SCSDT converter is provided having a self powered gate drive scheme for one or both of the power distribution and inverter stage and the combiner stage.

[00015] In embodiments, the SCSDT converter includes a level selection circuit (LSC) on the distributor side. In embodiments, the SCSDT converter includes a level selection circuit (LSC) on the combiner side. In embodiments, the SCSDT converter includes a level selection circuit (LSC) on both the combiner and distributor sides. In embodiments, the LSC is provided as a shift inductor level selection circuit (SILSC).

[00016] In embodiments, the SCSDT power conversion circuit is provided having a single input and selectable output. In embodiments, the SCSDT power conversion circuit is provided having a selectable input and a single output.

[00017] In embodiments, the SCSDT power conversion circuit is provided as a unity power factor ac-dc converter. In embodiments, the SCSDT power

conversion circuit is provided as a unity power factor ac-dc converter. In embodiments, the SCSDT power conversion circuit is provided as a dc-ac converter.

[0018] In embodiments, a switched-capacitor split-drive transformer (SCSDT) power conversion circuit includes a power distributor and inverter stage comprising n inverter and charge transfer cells. In one embodiment the inverter and charge transfer cells comprise decoupling capacitors, charge shuffling capacitors and 4n switches.

[0019] In embodiments, each of the n inverter and charge transfer cells comprises one or more decoupling capacitors (C_B); 2n-2 charge shuffling capacitors (Cs4n switches (S_w).

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features and advantages of the concepts, systems and techniques disclosed herein will be apparent from the following description of the

embodiments taken in conjunction with the accompanying drawings in which:

[0021] Fig. 1 is a block diagram of a power conversion circuit having a switched- capacitor split-drive transformer (SCSDT) power conversion architecture;

[0022] Fig. 1A is a block diagram of a power conversion circuit having a switched-capacitor split-drive transformer (SCSDT) and one or more level selection circuits;

[0023] Fig. 2A is a block diagram which illustrates an architecture of a power distributor and inverter stage;

[0024] Fig. 2B is a schematic diagram of an illustration implementation of a power distributor and inverter stage having the architecture shown in Fig. 2A;

[0025] Fig. 3A is a schematic diagram of a conventional single-drive-transformer structure; [0026] Fig. 3B is a schematic diagram of a parasitic capacitance model for the conventional single-drive-transformer structure shown in Fig.3A;

[0027] Fig. 4A is a diagram of a SDT transformer structure;

[0028] Fig. 4B is a parasitic capacitance model of the transformer structure shown in Fig.4A;

[0029] Fig. 5A is a diagram which illustrates an architecture of a parallel connected power combiner;

[0030] Fig. 5B is a schematic diagram of an illustrative implementation of a parallel connected power combiner having the architecture shown in Fig. 5A.

[0031] Fig. 6A is a diagram which illustrates an architecture of a series

connected power combiner;

[0032] Fig. 6B is a schematic diagram of an illustrative implementation of a series connected power combiner having the architecture shown in Fig. 6A.

[0033] Fig. 7 is a schematic diagram of an example split drive transformer conversion architecture;

[0034] Fig. 8 is a schematic diagram of a switch and gate drive implementation of a power distributor and inverter;

[0035] Figs. 9A and 9B illustrate an interleaved transformer winding structure;

[0036] Fig. 10 is a schematic diagram of an illustrative switch and gate drive implementation of the power combiner; [0037] Fig. 11 is a schematic diagram of an illustrative implementation of the SCSDT power conversion architecture with single input and selectable output;

[0038] Fig. 12 is a schematic diagram of a SDT power conversion architecture with centralized rectification;

[0039] Fig. 13 is a schematic diagram of a SDT power conversion architecture with half-bridge switching cells as both inverter and rectifier;

[0040] Fig. 14 is a schematic diagram which illustrates a self-powered gate drive technique for a power distribution and inverter stage such as the power distribution and inverter stage describes above in conjunction with Fig. 1 ; and

[0041] Fig. 15 is a block diagram of a unity power factor ac-dc converter that uses the SCSDT power conversion architecture.

[0042] Fig 16A is a schematic diagram of a shift inductor level selection circuit on the input side;

[0043] Fig. 16B is a block diagram of a power conversion circuit having a level selection circuit on one side only;

[0044] Fig. 17 is a schematic diagram of a shift inductor level selection circuit;

[0045] Fig. 8A is a boost type shift inductor level selection circuit having boost converter cells as level selectors;

[0046] Fig. 18B is a schematic diagram of a level selection circuit having boost converter cells as level selectors;

[0047] Fig. 19A is a buck type shift inductor level selection circuit having buck converter cells as level selectors; [0048] Fig. 19B is a schematic diagram of a level selection circuit having buck converter cells as level selectors;

[0049] Fig. 20 is a schematic diagram of a level selection circuit configured to be coupled on an output side of a power converter circuit;

[0050] Fig. 21 is a schematic diagram of an example variable -input fixed-output two-voltage-domain switched-capacitor split-drive-transformer power converter;

[0051 ] Fig. 22 is a schematic diagram of another embodiment of an example variable-input fixed-output two-voltage-domain switched-capacitor split-drive- transformer power converter; and

[0052] Fig. 23 is a schematic diagram of another embodiment of an example variable-input fixed-output two-voltage-domain switched-capacitor split-drive- transformer power converter.

[0053] The drawings are not necessarily to scale, or inclusive of all elements of a system, emphasis instead generally being placed upon illustrating the concepts, structures, and techniques sought to be protected herein.

DETAILED DESCRIPTION

[0054] The features and other details of the concepts, systems, circuits and techniques sought to be protected herein will now be more particularly described. It will be understood that any specific embodiments described herein are shown by way of illustration and not as limitations of the disclosure. The principal features of this disclosure can be employed in various embodiments without departing from the scope of the concepts sought to be protected. Embodiments of the present disclosure and associated advantages may also be understood by referring to the drawings, where like numerals are used for like and corresponding parts throughout the various views. [0055] Referring now to Fig. 1 , an architecture for a power converter 10 includes a power distributor and inverter stage 12, a split-drive transformer (SDT) stage 14 and a power combiner and rectifier stage 16. SDT stage 14 includes a

transformer structure having at least one magnetic flux linkage driven by multiple independent sources.

[0056] The power distributor (i.e., splitter) and inverter stage 2 has either or both of the following two functions. One function is to receive the overall input power and voltage from a source (e.g. from source/load 18-here shown in phantom since it is not properly a part of the power converter 10), condition it and distribute it to multiple paths to interface with the split-drive transformer stage 4. This includes, for example, taking input at a low frequency (e.g., dc, 60 Hz ac, etc.) and inverting the input into multiple sets of high-frequency ac drive waveforms that can interface with the transformer stage 14. Is should be noted that since converter 10 may operate in either direction, elements 18 and 20 are each indicated as source or loads (i.e. when element 18 is a source, element 20 is a load and vice-versa).

[0057] The other function of power distributor and inverter stage 12 is to maintain the variation of its outputs within a narrow range (e.g., voltage range) even if its input has relatively variations. Theoretically the architecture can handle arbitrary wide voltage range (0%-100%). In practical systems, a range of about 25% to about 100% (e.g. about 1 :4) can be achieved. This may reflect partial or complete preregulation of the voltages of this stage. This function enables the remainder of the converter to be optimized for a compressed operating range, leading to a higher efficiency of the overall system.

[0058] As noted above, SDT stage 14 is provided having a single magnetic flux path and receives a plurality of signals (e.g. preregulated voltage signals) at an input thereof from power distributor and inverter stage 12. SDT stage 14 functions to step up/down the signal level (e.g. voltage level) and electrically isolate the power distributor and inverter 12 from power combiner and rectifier 16 such that variations in a respective one of power distributor and inverter 12 or power combiner 14 do not affect operation and/or performance of the other.

[0059] Power combiner and rectifier 6 receives the signals (e.g. voltages) provided thereto from SDT stage 14 and combines the signals into an output provided to a load/source 20 (with load/source 20 being shown in phantom in Fig. 1 since it is not properly a part of the power converter circuit 10).

[0060] Detailed examples of illustrative power distributor and inventor stage 12, SDT stage 14 and power combiner and rectifier stage 16 will be provided herein below.

[0061] Referring now to Fig. 1A, a power converter 10' includes a first optional level selection circuit (LSC) 17a coupled between source/load 18 and power distributor and inverter stage 12'. Power converter 10' also includes a second, optional LSC 17b coupled between a power combiner and rectifier stage 16' and source/load 20.

[0062] LSC circuits each perform a level selection function.. The SDT

architecture splits the full input voltage range into multiple voltage domains. And the operation mode of the LSC circuit is determined by the domain in which the input voltage locates. For example, in the boost type LSC as shown in Fig. 18B, when the input voltage is between 20V~30V, S1 is controlled to regulate the source of S2 to be 30V. S2 is kept on, and S3 is kept off. When the input voltage is between 30V-60V, S2 is controlled to regulate the source of S2 to be 30V, S1 is kept off, and S3 is kept on. When the input voltage is between 60V 90V, S1 and S2 are kept off, and S3 is controlled to regulate the source of S3 to be 60V. (Other control methods are also applicable).

[0063] It should be appreciated that in some embodiments, power converter 10' includes both LSC 17a, 17b while in other embodiments power converter 10' includes only one of LSC 17a, 17b. Whether an input or output LSC is needed depends upon the needs of the particular application. When the application has wide input voltage range (or if it needs to take in and combine multiple input voltages), an input LSC is helpful. When the application has wide output voltage range (or if it needs to supply multiple output voltages), an output LSC will be useful.

[0064] Referring now to Fig. 2A, a level section circuit 11 is coupled to an illustrative switched-capacitor based implementation of a power distributor and inverter stage 12. Level section circuit 1 includes an n-port divider 24 having an input 23 configured to receive an input voltage V_in. Other implementations (i.e. other than switched - capacitor based implementations) are, of course, also possible. The advantage of an SC implementation is that one can nicely combine and reuse the switches of the SC circuits as half-bridge inverters. This

configuration also enables soft switching of all SC switches (in pure SC converters all switches are hard-switched). Whether soft-switching can or cannot be achieved depends, at least in part, upon the power/frequency and the size of the passive components.

[0065] Another possible embodiment is to have differential power processing cells as the power distributer/combiner stage. It should, of course, be

appreciated that such implementations require multiple magnetic components instead of one. Each of a plurality of divider outputs (here n outputs denoted 24a- 24n) may be selectively coupled (e.g. through corresponding ones of switches 26 - here n switches 26a-26n) to a corresponding one of a plurality of inverter cells (herein n inverter cells 28a-28n).

[0066] Each inverter cell 28a-28n is configured to selectively receive an input voltage at one of n input ports denoted K_xi - K_xn and in response thereto produce an output signal (e.g. an inverted voltage) at a port thereof (e.g. inverted voltages iN i - ViNVn at inverter cell ports denoted K_Yi - K_Yn. A balancer is coupled between each inverter cell. In the SC implementation, the power balancer is naturally embedded in the ladder SC circuits. The C_s4 (and other similar "flying capacitors") function as the power balancer in the SC implementation. [0067] One can also use "flying" inductors as power balancer device, and that is more like a resonant SC circuit or differential power processing circuit.

[0068] Referring now to Fig. 2B, a power distributor and inverter stage 12", which may be the same as or similar to stages 2 and 12' (Figs. 1 and 2A above) includes n full-bridge inverter and charge transfer cells. Each of the charge transfer cells comprise decoupling capacitors (C_B), 2n-2 charge shuffling capacitors (C_s) and 4n switches (S_w) where n is the number of switching cells. The number of input ports can be any number smaller than the total number of switching cells (inverters) As one function, this stage can act similarly to a two-phase ladder switched-capacitor voltage equalizer, such that all decoupling capacitor voltages C_B are equalized. There are n possible input points (K_Xi - K_Xn). Assuming the input voltage is V_in, and the m^th intersection (Kx_m) is selected as the input point (with the other terminal of V_in connected to the lowest-potential capacitor terminal), the voltages of inverter cells CerCs_m will each be V_in/m. All other capacitors will be maintained at V_in/m by the switched-capacitor charge transfer. In some implementations, one may select among any input point, while in others only a single input point may be provided. The number of input points one might select from depends upon a variety of factors including but not limited to voltage ranges to be managed and what subset of the selector switches K_ni-K_nn one implements.

[0069] The selection of the input point can be made to depend upon the input voltage. When the input voltage is high, K_Xi with larger /^' is selected to divide the high voltage across more cells. And when the input voltage is low, K_Xi with smaller / is selected to divide the voltage across fewer cells. As a result, the output voltage variation is reduced. The input voltage range across each potential input is optimally selected. One optimization goal is to reduce (and ideally minimize) the range over which the cell voltages vary. Other optimization goals are also possible. Other optimization goals are, of course, possible. One needs to make tradeoffs to balance the circuit complexity and performance. Theoretically, a circuit structure with more levels can perform better, with a higher complexity. [0070] Each decoupling capacitor (e.g. capacitor CBN) and the four connected switches (e.g. switches 42, 44, 46, 48) form a full-bridge inverter cell providing an ac drive voltage to interface with the split-drive transformer stage. Thus, n ac drive waveforms are provided to the split-drive transformer stage, each of which can be smaller in ac amplitude than would be realized with a single inverter.

[0071] It is noted that separate switches and topologies could be used for the voltage balancing function and the inverter function. The ladder SC configuration (all switches and capacitors in Fig. 2B) does the balancing and inverting at the same time. This would provide greater flexibility in topology and operation, e.g., by allowing different phases and switching times of the individual ac drives and/or by allowing different inverter circuit topologies to be applied. However, while desirable in some applications such variations would come at the expense of higher component count.

[0072] It is also noted that one could use a single-phase balancer configuration (i.e., not an interleaved one), and/or only use a single phase of the interleaved balancer to synthesize the inverter drive outputs (requiring a blocking capacitor in series with each inverter output). This would have the advantage of reducing the ac drive amplitudes produced by the inverter cells and - in some cases - reducing component count.

[0073] In addition to the elements to synthesize the ac waveform, each inverter cell may optionally include elements to provide filtering, voltage transformation, and - in some cases - to provide current sharing among the different inverter outputs. These could be impedance elements (e.g., series resonant tank) or two- port networks connecting between the inverter switch outputs and the transformer inputs (e.g., two-port filter networks or immittance converter networks). Placing an immittance converter network at the output of each inverter cell, for example, would ensure that equal voltages developed at the output of the inverter cells would drive equal currents into the transformer stage. Likewise, a series resonant tank could provide frequency shaping of the voltage at the transformer, provide frequency selectivity for control through frequency control, and provide some series impedance to help ensure current balance among the inverter outputs. Note that portions of such networks could be formed from transformer parasitic elements, such as inter-winding capacitances, leakage inductances, etc.

[0074] As noted above, the SDT stage operates to step up/down voltage provided thereto and provide isolation. In one embodiment, the split-drive transformer stage uses magnetic coupling to step up/down the voltage and provide isolation. In conventional single drive transformer structures, as shown in Fig. 3A the transformer has one primary winding and one secondary winding. In a planar transformer structure, windings may be implemented with flat copper planes stacked close to each other, resulting in significant parasitic capacitance.

[0075] Referring now to Figs. 3A and 3B a conventional single-drive transformer structure and a simplified lumped model of the parasitic components are shown. It should be appreciated that although the conventional transformer of Fig. 1 includes multiple primary windings, they belong to a single current path. The parasitic capacitance between primary windings and secondary windings is modeled as common-mode capacitance (C_cm)- The parasitic capacitance between two primary windings or two secondary windings is modeled as differential-mode capacitance (C-diff). These capacitances, together with Z_in and Z_cm, form a path for current to flow, which can yield loss. Moreover, the ac flows can distort the intended voltage transformation of the converter. Z_in may include impedances provided as part of the distribution stage, while Z_cm may include parasitic coupling, such as through the enclosure of the power converter. As switching frequency increases, the effects of these capacitive components become larger, and associated proximity-effect currents induce more loss.

[0076] Referring now to Fig. 4A, a spit-drive transformer structure includes n primary winding sets with the primary of each winding set driven by one of n inverter outputs of a power distributor and inverter stage such as that described below in conjunction with Figs. 1 , 2A and 2B. As described herein, split drive transformer structure corresponds to a transformer structure that has at least one magnetic flux linkage that are driven by multiple independent sources. The SDT structure reduces the loss resultant, at least in part, from the parasitic

capacitances described above in conjunction with Fig. 3. This is accomplished by the SDT structure reducing, and ideally eliminating, at least the parasitic capacitances typically associated with a conventional transformer structure.

[0077] It should be appreciated that rather than having a single primary winding and a single secondary winding as in conventional approach, the SDT structure described herein has a plurality n primary-secondary winding sets, with the primary of each winding set driven by one of the n inverter outputs of the power distributor and inverter stage. Each winding set provides identical turns ratio, and together they link a single dominant magnetic flux path. As illustrated in Fig. 4B, common-mode capacitances still exists in these winding-pairs, but owing to the distribution of the inverter function in the distribution stage, the common-mode components of the ac voltages driving currents through the capacitances are reduced, thereby reducing the current flows, reducing both loss and the impact on the voltage conversion function of the transformer stage.

[0078] Moreover, the split-drive transformer stage may be structured with the different winding sets (e.g., one for each drive input) interleaved. This can significantly reduce proximity effect loss in the transformer. The proximity effect can be significantly reduced by appropriately interleaving the windings. It should be appreciated that it is possible to interleave in a variety of different ways. In many applications, winding resistance and leakage inductance are the main considerations in selecting an interleaving techniques and structures. In some applications, thermal and mechanical constraints may also have a substantial impact in selecting an interleaving techniques and structures. Other factors, may also be considered.

[0079] Referring now to Fig. 4B a parasitic capacitance model 60 or the SDT transformer 50 of Fig. 4A includes common mode capacitances C_om and differential capacitors Cdiff- It should be appreciated that there are many ways to model, and to reduce the parasitic capacitance. [0080] Referring now to Fig. 5A, a power combiner and rectifier stage 62 which may be appropriate for use in a power converter such as that shown in Fig. 1 includes a plurality of synchronous rectifiers generally denoted by (here n rectifiers 64a-64n) with each rectifier 64a-64n having an input to accept voltages and outputs at which output voltages are provided. In the embodiment of Fig. 5A the outputs of each synchronous rectifier 64a-64n are coupled in parallel to provide a single output 65. In operation as part of a power converter, the power combiner and rectifier stage combines the n ac outputs voltages of the split-drive transformer stage into a single dc output voltage at terminal 65. If the output voltage is low, taking the secondary windings from the transformer and converting them to dc through synchronous rectifier structures connected in parallel at their outputs.

[0081] Referring to Fig. 5B, an illustrative implantation of a power combiner and rectifier stage 70 includes a plurality of synchronous rectifiers 72a-72n. Each synchronous rectifier includes a capacitor (e.g. one of capacitors CBI - C_BN) and a plurality of switches, here four switches 74a-74d (identified only in conjunction with inverter 72n for clarity). The switches operate to provide the inverting function as is generally known. Usually these switches are controlled symmetrically. Although asymmetric half-bridge inverters may also exist. It is, of course, possible to use frequency control.

[0082] Alternatively, if the output voltage is high, series connected output rectifier structure as shown in Fig. 6 fits better. Those of ordinary skill in the art will appreciate that there are many ways of interconnecting rectifier outputs. There are likewise many other possible ways of implementing the power combiners (e.g. half-bridge vs. full-bridge, centralized vs. distributed), allowing tradeoffs to be made. Tradeoffs are usually made between component counts, efficiency, parasitics and size. Tradeoffs also strongly depend on applications.

[0083] One function of the power combiner and rectifier stage is to rectify the individual (high-frequency) outputs of the split-drive transformer stage. One may individually rectify the outputs of each of the transformer winding sets and combine their outputs at dc (in series, parallel, or with some other combination). Alternatively, the ac outputs of the transformer stage may be combined and rectified together with a single rectifier structure.

[0084] The power combiner stage may also include other elements before the one or more rectifiers. Cascaded with the secondary winding of each transformer winding set, one may optionally include elements to provide filtering, voltage transformation, and - in some cases - to provide current sharing among the different transformer secondaries. These could be impedance elements (e.g., series resonant tank) or two-port networks connecting between the secondary winding outputs and the input(s) to the rectifier(s), such as, two-port filter networks or immittance converter networks. Placing an immittance converter network at the output of each transformer secondary, for example, would ensure that equal voltages developed at the output of the inverter cells would drive equal currents into the transformer stage. Likewise, a series resonant tank could provide frequency shaping of the voltage at the transformer, provide frequency selectivity for control through frequency control, and provide some series impedance to help ensure current balance among the transformer secondaries. Note that portions of such networks could be formed from transformer parasitic elements, such as interwinding capacitances, leakage inductances, etc.

[0085] Referring now to Fig. 7 an illustrative power converter appropriate for use as a step down dc-dc converter in telecom base station applications. Power converter 80 includes a power distributor and inverter 82, coupled to an SDT stage 84 which in turn is coupled to a power combiner and rectifier stage 86.

Power converter 70 is configured to receive voltages in the range of about 36V to about 72V, V_in and supply at an output thereof an output voltage V_out in the range of about 5V to about 3.3V.

[0086] The power distributor has four full-bridge cells and two input options.

When 36V<V_in<48V, K_xi is selected as the input; and when 48V<V_in<72V, is selected as the input. Under this setup, the operating range of each full-bridge cell is between 12V ~18V, smaller than the range between 9V-18V if Κχ2 is always used as the input. [0087] Referring now to Fig. 8, a power distributor and inverter circuit 100 is implemented via gate and switch drive technology. This implementation enables a fully integrated solution of the gate drive circuit. Power for the gate drive circuit is obtained locally, while the gate drive signal is naturally boot-strapped. No additional magnetic/optical coupling is required. A stacked boot-strap structure is selected here, although many other possibilities exist.

[0088] Referring now to Figs. 9 and 9B, an illustrative transformer structure 110 is shown. The transformer structure of this example design is a 12 layer planar transformer having four 2:1 winding pairs (sets) that dominantly share a single magnetic flux path. In order to reduce the proximity effect, the primary and secondary windings are interleaved (such that each winding set is an interleaved structure). Other interleaving techniques and structures may also be used. The positions and orientations (winding directions) of the sections of the primary windings of adjacent winding sets are positioned in a manner that reduces the the capacitive charge injection from one winding set to another due to the parasitic capacitance between two primary windings. Thus, for example, physically close windings adjacent primaries are laid out such that their individual ac swings are similar, such that capacitive charge injection from one set primary winding to another set primary winding is reduced. This implementation also uses the leakage inductances of the transformer, L_ri~L_r4, (e.g., the leakage inductance between the primary and secondary of each winding set) as an impedance for power control and for helping to ensure current sharing among winding sets.

[0089] Referring now to Fig. 0, a power combiner and rectifier stage 120 includes four full bridge synchronous rectifiers 112a-112d connected with their outputs in parallel. This stage uses eight half-bridge gate drives 114a-114d and 116a-116d to control the different rectifiers 112a-112d independently; and applies phase-shift control to balance one or more of power and current among the multiple transformer winding sets. This control handle can also be used to determine where magnetizing current flows in the transformer, helping to mitigate proximity effect. Likewise, frequency control or net phase control between the power divider and inverter stage and the power combiner and rectifier stage can be used to control total power flow and regulate the system output. Other control means, such as on-off control can likewise be used to regulate the system output.

[0090] The voltage regulation of the proposed converter architecture can be implemented in multiple ways, depending upon the selected impedance

controlling component. For example, if the impedance controlling component is an inductor (e.g., using the primary-to-secondary leakages of the individual winding sets as impedances for power control), the net power flow through the converter can be controlled in a manner similar to a dual-active-bridge (DAB) converter with phase-shift control. If an additional series capacitor is provided, such impedances could be used to form a set of series resonant tanks, and the net power flow in the converter could be controlled in a manner similar to that of a series-resonant converter combining frequency control and phase shift control. Both the DAB and the series resonant converter enable ZVS of all the switches.

[0091] After reading the broad concepts disclosed herein, one of ordinary skill in the art will appreciate that there are many extensions of the proposed SDC architecture, allowing tradeoffs to be made. Several examples are presented here as conceptual introductions.

[0092] One alternate implementation of the SCSDT power conversion

architecture is described below in conjunction with Fig. 11.

[0093] Referring now to Fig. 1 , an implementation of the SCSDT power conversion architecture which "flips" the inputs and the outputs of the illustrative circuits and systems described herein is shown. That is, Fig. 11 shows a power conversion circuit using the SCSDT power conversion architecture having a single input and selectable output.

[0094] It should be noted that, in general, the architecture illustrated in Fig. 1 may flow power in either or both directions as compared to the above description, with circuit structures used appropriately as inverters and rectifiers, respectively. Four substantially identical high-frequency-link converters drive a split-drive transformer having a single dominant magnetic flux path, followed by a converter structure incorporating switched capacitor voltage equalizer which combines the power. One can select from among the voltages of this structure to provide an output voltage.

[0095] Referring now to Fig. 12, a converter having an SCSDT architecture includes a centralized rectification stage. Instead of rectifying the outputs before combining them, this implementation combines outputs in ac and rectifies them in a centralized rectifier.

[0096] The power distributor and inverter and power combiner and rectifier stages may be implemented with other topologies. Half bridge inverters and half- bridge rectifiers may also be utilized in this architecture, for example, as illustrated in Fig. 13.

[0097] Referring now to Fig. 13, : a PAL power conversion architecture includes half-bridge switching cells.

[0098] Referring now to Fig. 14 a power converter having the SCSDT architecture includes a self powered gate drive structure for the power distribution and inverter stage. The self-powered gate drive structure shown in Fig. 14 becomes appealing when the voltage range of each of the full-bridge cells is between 5V~15V range (assuming a MOSFET implementation) since in this voltage range each half- bridge gate drive is powered from the corresponding bypass capacitors, eliminating the requirement auxiliary isolated power supplies. Other voltage ranges may be used for implementations other than MOSEFT implementations.

[0099] Referring now to Fig. 15, shows the architecture of a unity power factor ac-dc converter that uses the SCSDT power conversion architecture. This could also be extended to be a dc-ac inverter by reversing the power flow direction and making appropriate changes to each stage. The major change to accomplish this is that the user needs to make sure the switch polarity is correct (if all switches are bidirectional, then no modification is needed). The other modification is to select the appropriate transformer turns ratio.

[00100] Fig 16A is a schematic diagram of a shift inductor level selection circuit (SILSC) 17a' which may be the same as or similar to SILSC 17a described above in conjunction with Fig. 1A. This SILSC has one inductive element (here illustrated as an inductor L_in) and two switching elements (here, illustrated as single pole-single throw switches S_H, S_L although other switching elements could also be used). The inductive element functions as an energy storage device and carries the input current. The two switching elements redistribute the current into two ports of the switched capacitor circuit. The duty ratio of the two switches is controlled such that the voltage at the two output node are regulated to the desired voltage.

[00101] Fig. 16B is a block diagram of a power conversion circuit having a single level selection circuit. In this design, the output LSC is not needed because the circuit shown in Fig.16A is designed for a regulated single output voltage

application.

[00102] Fig. 17 is a schematic diagram of at least a portion of a power converter circuit which includes shift inductor level selection circuit 17a" which may be the same as or similar to SILSC 17a described above in conjunction with Fig. 1A.

SILSC 17a" has one inductive element (here illustrated as inductor L_in' and three bidirectional switching elements (here illustrated as three bidirectional switches Κχι, Κχ2, Κχ₃). The switch states of the three switches depend on the input voltage.

[00103] Fig. 18A is a boost type shift inductor level selection circuit having boost converter cells as level selectors. The maximum voltage that the current feed in is higher than the highest input voltage.

[00104] Fig. 18B is a schematic diagram of a level selection circuit having boost converter cells as level selectors as described above. [00105] Fig. 19A is a buck type shift inductor level selection circuit having buck converter cells as level selectors. The maximum voltage that the current can feed in from is lower than the highest input voltage.

[00106] Fig. 19B is a schematic diagram of a level selection circuit having buck converter cells as level selectors. When V1<Vx<V2, Kx2, Kx6 are switched as a half bridge, Kx5 is kept on, and all other switches are off. In this manner, Kx2, Kx6 and the inductor function as a buck converter. When V2<Vx<V3, Kx1 , Kx5 are switched as a half bridge, Kx4 is kept on, and all other switches are off. In this manner, Kx1 , Kx5 and the inductor function as a buck converter. When V3<Vx, Kx2, Kx4 are switched as a half bridge, Kx3 is kept on, and all other switches are off. In this manner, Kx2, Kx4 and the inductor function as a buck converter.

[00107] Fig. 20 is a schematic diagram of a level selection circuit configured to be coupled on an output side of a power converter circuit. By reconfiguring the output switches, the output voltage can be any value larger or equal to the minimum voltage of the three connected node, and smaller or equal to the maximum voltage of the three connected node.

[00108] Referring now to Fig. 21 an illustrative variable -input fixed-output two- voltage-domain switched-capacitor split-drive-transformer power converter includes a boost-type level selection circuit on an input side. Boost-type level selection circuit comprises a pair of switching elements (here illustrated as transistors Q1 , Q2) and an inductive element (here illustrated as an inductor L1 ). Coupled to the level selection circuit is a two level power splitter and inverter provided from transistors Q3, Q4, Q5, Q6 and capacitors C1 , C2, C5. It should be appreciated that while this illustrative embodiment shows elements Q1-Q10 as transistors, any type of switching element having suitable characteristics may be used. Similarly, any type of inductive element may be used in place of the inductors and any type of capacitive element may be used in place of the capacitors. [00109] A pair of dc blocking elements, here illustrated as capacitors C3, C4, are coupled between the power splitter and inverter and a first side of a split drive transformer. The dc blocking capacitors C3, C4 are selected having capacitance values to prevent the transformer from saturation.

[00110] In this illustrative embodiment, the split drive transformer is provided having two primary windings and two secondary windings. The primary to secondary transformer turns ratio is n1 :n2 (T1 , T2). A centralized full bridge rectifier provided from switching elements (here, illustrated as transistors Q7, Q8, Q9, Q10) is coupled between a second side of the split drive transformer and a load R1.

[00111] In operation, transistors Q3, Q4 are operated as a half bridge with a 50% duty ratio. Transistors Q5, Q6 are operated as a half bridge with a 50% duty ratio. The voltages of C1 , C2 and C5 are equal to each other. As a result, V2=2xV1.

[00112] It should be appreciated that in this illustrative embodiment, the input voltage Vin should be larger than V1 and smaller than V2, V1<Vin<V2.

Transistors Q1 and Q2 are controlled such that V1 and V2 are regulated to desired voltages.

[00113] It should be appreciated that voltage V1 should preferably be regulated to a value corresponding to approximately 2Vout*n1/n2 and voltage V2 should preferably be regulated to be a value corresponding approximately to 4Vout^*n1/n2.

[00114] Transistors Q7-Q10 are controlled to operate as a synchronous rectifier and they can be phase shifted with transistors Q3-Q6 to provide voltage regulation and soft-switching.

[00115] Referring now to Fig. 22, in which like elements of Fig. 21 are provided having like reference designations, another embodiment of an illustrative variable- input fixed-output two-voltage-domain switched-capacitor split-drive-transformer power converter is shown. In this illustrative embodiment the variable-input fixed- output two-voltage-domain switched-capacitor split-drive-transformer power converter includes a boost-type level selection circuit which is different than the boost-type level selection circuit described above in conjunction with Fig. 21. The boost-type level selection circuit is able to further expand the input voltage range (i.e. expand the input voltage range beyond that which the selection circuit of Fig. 21 can provide). It should be appreciated that while the embodiment of Fig. 22 has higher component count than the embodiment of Fig. 21 , the embodiment of Fig. 22 can handle wider range of input voltages than the embodiment of Fig. 21.

[00116] In this circuit, input voltage Vin can be any value between GND and voltage value V2. When the value of input voltage Vin is between a reference potential corresponding to ground (for example) and a voltage value V1 (i.e.

GND<Vin<V1 ), transistor Q1 is kept on, transistor Q2 is kept off, and transistors Q11 and Q12 are controlled such that voltage V1 is regulated to desired values. When the value of input voltage Vin is between a reference potential

corresponding to a voltage value V1 (for example) and a voltage value V2 (i.e. V1 <Vin<V2), transistor Q11 is kept off, transistor Q12 is kept on, and transistors Q1 and Q2 are controlled such that voltage values V1 and V2 are regulated to desired values. Other components of the variable-input fixed-output two-voltage- domain switched-capacitor split-drive-transformer power converter of Fig. 22 are operated substantially in the same way as described above in connection with the variable-input fixed-output two-voltage-domain switched-capacitor split-drive- transformer power converter of Fig. 21.

[00117] Referring now to Fig. 23, an illustrative variable-input fixed-output three- voltage-domain switched-capacitor split-drive-transformer power converter comprises a split drive transformer having three primary windings T1a, T2a and T3a and three secondary windings T1 b, T2b and T3b.

[00118] Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts, structures and techniques may be used.

Accordingly, it is submitted that that scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims.

Claims

1. A power converter having an input and an output, the power converter comprising:

a power distribution and inverter stage having an input coupled to the input of the power converter and a plurality of outputs;

a split drive transformer stage having a plurality of inputs coupled to corresponding ones of the plurality of outputs of said power distribution and inverter stage and having a plurality of outputs, said split drive transformer stage including a transformer structure having at least one magnetic flux linkage driven by multiple independent sources; and

a power combiner and rectifier stage having a plurality of inputs coupled to respective ones of the plurality of outputs of said split drive transformer stage and an output coupled to the output of the power converter.

2. The power converter of claim 1 wherein said power distribution and inverter stage further comprises a level selection circuit.

3. The power converter of claim 1 wherein said power combiner and rectifier stage further comprises a level selection circuit.

4. The power converter of claim 1 further comprising:

a first level selection circuit coupled between the input of the power converter and input of the power distribution and inverter stage; and

a second level selection circuit coupled between the output of the power combiner and rectifier stage and the output of the power converter.

5. The power converter of claim 1 further comprising at least one of:

6. The power converter of claim 5 wherein at least of said first and second level selection circuit is provided as a shift inductor level selection circuit (SILSC).

7. The power converter of claim 5 wherein at least of said first and second level selection circuits is provided as a boost-type level selection circuit.

8. The power converter of claim 7 wherein said power distribution and inverter stage comprises a two level power splitter and inverter.

9. The power converter of claim 7 further comprising one or more blocking capacitors coupled between said power distribution and inverter stage and said split drive transformer stage, said one or more blocking capacitors having a capacitance selected to prevent said split drive transformer stage transformer from saturation.

10. The power converter of claim 7 wherein said split drive transformer stage comprises a split drive transformer having a pair of primary windings and a pair of secondary windings and wherein the primary to secondary transformer turns ratio is n1 :n2.

11. The power converter of claim 7 wherein said power combiner and rectifier stage are provided as a centralized full bridge rectifier.

12. The power converter of claim 1 wherein said power combiner and rectifier stage is provided having a parallel output.

13. The power converter of claim 1 wherein said power combiner and rectifier stage is provided having a series output.

14. The power converter of claim 1 wherein said split drive transformer stage is provided having an interleaved configuration.

15. The power converter of claim 1 wherein said power distribution and inverter stage comprises one or more half bridge switching cells.

16. The power converter of claim 1 wherein said power combiner and rectifier stage comprises one or more half bridge switching cells.

17. The power converter of claim 16 wherein said power combiner and rectifier stage comprises a plurality of switching elements configured such that said combiner and rectifier stage are capable of operating as a synchronous rectifier.

18. The power converter of claim 16 wherein:

said power distributor and inverter stage comprises switching elements; and

said switching elements of said combiner and rectifier stage can be phase shifted with said switching elements of said power distributor and inverter stage to provide voltage regulation and soft-switching.

19. The power converter of claim 11 wherein:

said power distributor and inverter stage comprises a first set of switching elements Q3, Q4 which form a first half bridge circuit and a second set of switching elements Q5, Q6 which form a second half bridge circuit wherein said first half bridge circuit is capable of operation with a 50% duty ratio and the second half bridge circuit is capable of operation with a with 50% duty ratio; and said first level selection circuit comprises a first set of switching elements Q1 , Q2 coupled to an inductive element and wherein the first set of switching elements of said first level selection circuit are capable of being controlled so as to provide first and second regulated voltages V1 , V2 to inputs of said first and second half bridge circuits.

20. The power converter of claim 19 wherein:

an input voltage Vin is larger than the first regulated voltage V1 and smaller than the second regulated voltage V2 such that, V1<Vin<V2; the first regulated voltage V1 is regulated to be approximately

2Vout^*n1/n2 where n1 and n2 are the turns ratio of the split drive transformer and Vout is the voltage at the output of the power converter; and

the second regulated voltage V2 is regulated to be approximately

4Vout^*n1/n2.

21. The power converter of claim 20 wherein said power combiner and rectifier stage comprises a plurality of switching elements configured such that said combiner and rectifier stage are capable of operating as a synchronous rectifier.

22. The power converter of claim 21 wherein:

said power distributor and inverter stage comprises switching elements; and